1. Technical Field
The present invention relates in general to a docking device for a portable computer and in particular to a docking device for a portable computer at which a portable computer is loaded and fixed, which is electrically connected to the portable computer and which expands the various functions of the portable computer. Still more particularly, the present invention relates to a docking device for a portable computer in which radiated emission noise can be reduced easily and inexpensively.
2. Description of the Related Art
Portable computers such as notebook-type personal computers, which are structured so as to be compact and light-weight in view of the portability thereof, and docking devices for portable computers, which are connected mechanically and electrically to a portable computer and which expand various functions of the portable computer, have become popular in recent years. A portable computer and docking device are connected electrically for signal transmission between the docking device and the personal computer. A connector located at the rear surface of the portable computer and a connector located within the docking device contact each other to establish an electrical connection for signal transmission. The bodies of a portable computer and a docking device are both formed from electrically conductive materials such as carbon and nickel/copper (Ni--Cu) plating and both contain electrically conductive members such as circuit wiring. Therefore, when the portable computer and the docking device contact each other only at the connectors for signal transmission, a circuit is formed which is equivalent to a dipole antenna. In the equivalent circuit, the source of noise is the region of the connectors for signal transmission and the circuit elements include the body of the portable computer, the electrically conductive members accommodated therein, the body of the docking device, and the electrically conductive members accommodated therein. A problem arises in that when an electric potential difference arises between these elements, displacement current flows, emissions are radiated from the elements, and EMI (electromagnetic interference) occurs.
Conventionally, a sponge, which is coated with an electrically conductive material, has been interposed between the docking device for the portable computer and the portable computer so as to prevent EMI.
However, the body of the portable computer and the body of the docking device are coated so that the surfaces thereof are protected. Because the coated portions act as insulation, radiated emission noise cannot effectively be suppressed by the above structure.